Glow plugs are used to assist ignition in internal combustion engines, as for non-autoignitable fuels. Although a glow plug portion exposed to combustion is typically constructed of silicon nitride, the life of a glow plug is relatively short due to corrosion and erosion of the silicon nitride at the elevated temperature at which a glow plug must be maintained to sustain good combustion.
It is known to provide protective tubular shields of metal or ceramic circumferentially surrounding a glow plug along its length. The shield is spaced from the glow plug and is perforated and/or open at an axial end for access of combustible mixture to the glow plug. It is also known to protect a silicon nitride glow plug by coating the plug with a refractory metal oxide and to provide a glow plug with a combustion promoting catalyst so that the glow plug temperature may be reduced.